Instrument panels in vehicles include instruments that indicate various conditions of the vehicles. For example, a passenger car or an over-the-highway truck typically includes a speedometer that indicates vehicle speed and may include instruments that indicate fuel remaining and coolant temperature, among others.
Such instruments may be analog or digital. An analog instrument typically includes a mechanical indicator, such as a pointer, that moves with respect to a fixed scale. A digital instrument typically includes an electronic display, such as a liquid crystal display (LCD), an electroluminescent or plasma display, or arrays of light-emitting diodes or other light emitters, on which are presented changeable alphanumeric characters or an indicator that changes with respect to a fixed scale.
For either of these types of display, the units of measurement of the indicated parameter are predetermined and may be pre-printed on a bezel or other structure near the indicator or display or may be presented on the electronic display. For example, an analog speedometer may include an indicator needle that rotates with respect to fixed overlay scales in units of miles per hour (mph) and of kilometers per hour (kph).
Several vehicle instruments measure quantities that can have different units, depending on the location of the vehicle. English and metric scales are noted above in connection with a speedometer, but other scales may be in local use. For example, fuel volume may be indicated in English, metric, and/or Imperial units, for example.
Presenting information in measurement units that are appropriate to the location of a vehicle can be important for a number of reasons. For example, a truck driver may be less likely to comply with local speed limits and to avoid running out of fuel if the truck's speedometer and fuel gauge display their information in units different from the units of local speed limit and distance signs. This would improve the safety of the operation of the vehicle.
Accordingly, vehicle manufacturers which sell products world-wide may stock at least two different speedometers, at least two different fuel gauges, etc. to accommodate use of the English and metric measurement systems. As a lower-cost alternative, manufacturers have developed instruments with overlays that include more than one scale, as noted above, with one or the other being the primary scale that has larger characters. An overlay is typically an inked surface that, with backlighting, displays information to the driver with increased contrast ratio and visibility. For example, an overlay with a primary or only miles-per-hour scale is used in speedometers for vehicles that are sold in countries that use the British/English measurement system, and an overlay with a primary or only kilometers-per-hour scale is used in speedometers for vehicles that are sold in countries that use the metric measurement system.
The result of these considerations is a complex electronic instrument cluster that is defined, at least partially, by something as small as the “ink” on the overlay, leading to two different sets of part numbers for what are substantially identical parts that have the same function or show the same information. The different “ink” on these different parts is the different scales (e.g., English or metric) of speed, temperature, pressure, and other gauges. In essence, the clusters are identical except for the overlays.
Digital reconfigurable displays have been developed that present graphic representations of traditional indicators and scale overlays, thereby allowing several different gauges to be presented on one display. One type of reconfigurable display has a transparent electroluminescent display that presents different scales and a mechanical indicator positioned behind the scale display. Such digital reconfigurable displays normally permit a manufacturer to select different gauges to be displayed, such as speed, battery condition(s), oil pressure, water temperature, etc., with appropriate scales depending on the model and/or market of the vehicle.
Some instruments even allow an end user, like a vehicle driver, to toggle between a miles per hour mode where a miles per hour scale is displayed and a kilometers per hour mode where a kilometers per hour scale is displayed. U.S. Pat. No. 5,696,704 to Semrau and No. 4,284,028 to Swanburg describe speedometers having single scales and mechanisms that re-position the pointers according to measurement units selected by the drivers.
U.S. Pat. No. 6,353,781 to Spivak, for example, describes a marine speedometer that uses a standard output of a position-determining navigation unit, such as a LORAN or Global Positioning System (GPS) receiver. Speed information is received from the navigation unit in knots per hour and is shown on a display. A push-button switch causes a microprocessor to convert the speed information from knots to miles per hour for display.
Patent Abstracts of Japan Publication No. 07294624 describes a computer having navigation software and being connected to a GPS receiver. In response to a command, GPS data in the form of miles and world time is converted into a Tokyo system, e.g., kilometers and Japan time.
These kinds of prior devices are not ideal for vehicle instruments that measure quantities that can have different units, depending on the location of the vehicle. The pixels of a low-cost digital display do not define numeric characters that are as “crisp” or well defined as the characters stenciled into an overlay of an analog display, and so such gauges are often deemed unsatisfactory unless an expensive high resolution display is used. In addition, sun glare has a greater effect on digital displays than traditional analog displays.
Another important drawback of prior devices arises from the changeability of the desired “primary” scale in vehicles that operate in parts of the world like North America, where at one minute the “primary” scale should be English units and at the next minute the “primary” scale should be metric units as vehicles cross the border between the U.S. and Canada. A speedometer might have dual scales, i.e., a scale for miles per hour and a scale for kilometers per hour, but both scales are usually visible simultaneously and one of the two scales is always primary. Drivers must thus be alert to look at the proper scale as they drive in one country or the other, which increases the chance of confusion and inadvertent vehicle speed and other operational errors, decreasing vehicle safety.